Introduction to conjugate acids and bases. Created by Sal Khan.
Chemistry on Khan Academy: Did you know that everything is made out of chemicals? Chemistry is the study of matter: its composition, properties, and reactivity. This material roughly covers a first-year high school or college course, and a good understanding of algebra is helpful.
An introductory college-level chemistry course that explores topics such as atoms, compounds, and ions; chemical reactions and stoichiometry; ideal gases; chemical equilibrium; acids and bases; kinetics; thermodynamics; redox reactions and electrochemistry; and a whole lot more!